MCP discovery requires at least one search method (BM25 or r

Error message

MCP discovery requires at least one search method (BM25 or regex).

What it means

Validation error thrown in handleSave (web/frontend/src/components/config/config-page.tsx:329) when MCP is enabled, MCP discovery is enabled, but neither BM25 nor regex discovery is selected. Discovery needs at least one search backend to find MCP servers, so the combination is rejected client-side before the config PATCH is built.

Source

Thrown at web/frontend/src/components/config/config-page.tsx:329

      if (configDirty) {
        const workspace = form.workspace.trim()
        const dmScope = form.dmScope.trim()

        if (!workspace) {
          throw new Error("Workspace path is required.")
        }
        if (!dmScope) {
          throw new Error("Session scope is required.")
        }

        if (
          form.mcpEnabled &&
          form.mcpDiscoveryEnabled &&
          !form.mcpDiscoveryUseBM25 &&
          !form.mcpDiscoveryUseRegex
        ) {
          throw new Error(
            "MCP discovery requires at least one search method (BM25 or regex).",
          )
        }

        const maxTokens = parseIntField(form.maxTokens, "Max tokens", {
          min: 1,
        })
        const contextWindow = form.contextWindow.trim()
          ? parseIntField(form.contextWindow, "Context window", { min: 1 })
          : undefined
        const maxToolIterations = parseIntField(
          form.maxToolIterations,
          "Max tool iterations",
          { min: 1 },
        )
        const toolFeedbackMaxArgsLength = parseIntField(
          form.toolFeedbackMaxArgsLength,
          "Tool feedback max args length",

View on GitHub (pinned to 49183d7e8d)

Solutions

Re-check at least one of 'BM25' or 'regex' in the MCP discovery options
If you do not want discovery at all, uncheck 'MCP discovery enabled' instead of unchecking both methods
If you do not want MCP at all, uncheck 'MCP enabled' and both sub-toggles become irrelevant

Defensive patterns

Strategy: validation

Validate before calling

if (
  form.mcpEnabled &&
  form.mcpDiscoveryEnabled &&
  !form.mcpDiscoveryUseBM25 &&
  !form.mcpDiscoveryUseRegex
) {
  setFieldError("MCP discovery requires at least one search method (BM25 or regex).")
  return
}

Try / catch

try {
  await handleSave()
} catch (err) {
  if (err instanceof Error) setError(err.message)
}

Prevention

Use a checkbox group that prevents unchecking the last selected method
Auto-uncheck 'discovery enabled' when both methods are off, making the state unreachable
Show a hint under the discovery section listing which methods are active

When it happens

Trigger: Checking both 'MCP enabled' and 'MCP discovery enabled' while unchecking 'Use BM25' and 'Use regex' in the MCP discovery section, then saving.

Common situations: User disables regex to avoid heavy scanning, then also unchecks BM25 not realizing it was the last method; toggling options after loading a config where both were already off; misreading BM25 as optional telemetry.

Related errors

AI-assisted analysis of sipeed/picoclaw@49183d7e8d (2026-08-15). Data as JSON: /api/errors/1095054653bbdb2d. Report an issue: GitHub.